1. Field of the Invention
The present invention relates to a method and apparatus for positioning diaphragms in vertical slotted walls which are supported by a suspension, with respective diaphragm sections being lowered into the support suspension of the sealing wall mass.
2. Description of the Prior Art
Diaphragms or thin sheets are often installed as additional seals in vertical sealing walls, which are generally produced as slotted walls supported in suspensions. Such sealing slotted walls are particularly utilized in foundation work and water structures, but also for the vertical sealing of dumps. The sealing wall can be produced in a single or dual phase system. In the single phase system, either cement or some other hardening material is added to the support suspension of bentonite and water, with this suspension at the same time representing the final sealing wall mass. In the dual phase system, the actual support suspension of water and clay having thixotropic properties, such as bentonite, is replaced by the remaining sealing wall mass, such as concrete.
The diaphragm or thin sheet is predominantly positioned in the center of the slotted wall suspension as long as the latter has not yet hardened. The diaphragms are generally made of synthetic materials, such as PVC, PE, PP, or of thermoplastic elastomers on a base of natural or synthetic rubber. The positioning of the diaphragm in the support suspension is predominantly effected by weighting the bottom edge with steel sections or the like, and/or by using frames with which the diaphragm is forced into the support suspension.
In an article by Dipl.-Ing. Jaroslav Verfel, which appeared in TIS 10/82, the difficulties involved with the introduction of the diaphragm are explained in detail. The thin sheets, which are under buoyancy, can be positioned to a slotted wall depth of 10 m only at great technical expense. In particular, the viscosity of the suspension, expressed in the shearing strength .tau..sub.0, increases with time, and with the use of a single phase system can within 24 hours exceed ten times the value of the fresh suspension mixture. With the use of a support suspension exclusively of bentonite and water, the viscosity of the suspension increases due to the thixotropic properties of the bentonite/water mixture. If the suspension in the slot settles, the platelet-like stratified silicates of the bentonite form a "house of cards" structure due to the different electrical charges of the surfaces and the edges. The edges or boundary of the slotted wall are supported by this "house of cards" structure.
It is an object of the present invention to provide a method which considerably simplifies the introduction of the diaphragm into the slotted wall. It is a further object of the present invention to provide an apparatus for effecting this facilitated introduction.